docs: def _validate_cidr(self, rule):
          """Validate the cidr block in a rule.
  
          Returns:
              True: Upon successful completion.
  
          Raises:
              SpinnakerSecurityGroupCreationFailed: CIDR definition is invalid or
                  the network range is too wide.
          """
          try:
              network = ipaddress.IPv4Network(rule['app'])
          except (ipaddress.NetmaskValueError, ValueError) as error:
              raise SpinnakerSecurityGroupCreationFailed(error)
  
          self.log.debug('Validating CIDR: %s', network.exploded)
  
          return True